In the presence of catalysts, curable organosilicone compositions undergo hydrosilation, a reaction involving the addition of a silicon-hydrogen bond across a pair of aliphatic carbon atoms linked by multiple bonds. Reactions of this type are catalyzed by metals, most notably platinum (Pt), rhodium (Rh), iridium (Ir), and palladium (Pd), and compounds thereof. Hydrosilation has found widespread use in the production of silicone materials and organosilanes. Platinum-containing hydrosilation catalysts are known in the art and have been described in numerous patents, such as U.K. Patent Application GB No. 2,019,426 A, German Pat. No. 1,165,028, and U.S. Pat. Nos. 2,823,218, 3,814,730, 3,715,334, 3,516,946, 3,474,123, 3,419,593, 3,220,972, 3,188,299, 3,178,464, and 3,159,601. These catalysts often suffer from a number of disadvantages: they may be subject to "poisoning" in the presence of certain common materials; they may lack sufficient solubility or dispersibility in organic reaction media; they may be inefficient in promoting a reaction; and in their presence addition curable organosilicone compositions may lack stability and not exhibit satisfactory pot life.
U.S. Pat. No. 3,188,299 discloses nitrogen-containing compounds which are used with a platinum-containing catalyst to reduce or temporarily inhibit its activity in the presence of an alkenyl polysiloxane and a hydrogen polysiloxane. Although this patent discloses pyrazine as a useful ligand, the proportion of ligand to platinum catalyst used is considerably greater than Applicants' and thereby gives an entirely different product.
Other patents teaching hydrosilation nitrogen- and platinum-containing catalysts are U.K. Patent Application GB No. 2,019,426 A and German Pat. No. 1,165,028. The latter discloses trans-(pyridine)(ethylene).PtCl.sub.2 as an effective hydrosilation catalyst. U.K. Patent Application GB No. 2,019,426 A teaches a process for the addition of a silicon-bonded hydrogen atom to an aliphatic multiple bond, which comprises carrying out the addition in the presence of a catalyst which comprises at least one halogen-platinum complex selected from those of the general formulae A.sub.2 PtX.sub.2 and C.sub.3 H.sub.6 PtB.sub.2 X.sub.2, in which formulae each A denotes a pyridine ring that is substituted by 1 or 2 alkyl radicals having 1 to 3 carbon atoms, and each X denotes a halogen atom, and each B denotes a 5- or 6-member unsubstituted or substituted heterocyclic ring having 1 to 2 hetero atoms or B.sub.2 denotes two such rings joined together. Neither of these patents discloses a platinum catalyst that has the polynitrogen-containing single or fused ring structure which Applicants have discovered is important in providing increased stability and longer pot life to addition curable organosilicone compositions.